The present invention relates to the field of centrifugal impact crushers where a plurality of impeller blades are radially mounted adjacent the rim of a rapidly spinning horizontally-supported turntable. These impeller blades ensure that solid material thrown from the spinning turntable, such as rocks, are radially directed outwardly for breakage against anvils that are mounted on the walls of a surrounding container. More particularly, the present invention relates to an apparatus for mounting the impeller blades to the turntable.
In Ackers, U.S. Pat. No. 4,090,673, apparatus for mounting impeller blades to the turntable of a centrifugal impact crusher are shown. Each apparatus includes a bracket, fixedly joined to the turntable, having an upright mounting face in which an opening is formed. The impeller block, along the front of which the blade is formed, is positioned with its back against this mounting face so that a nub portion projecting from the back of the block is received through the opening formed in the mounting face. The impeller block is then detachably secured to the bracket by a pin which releasably slides through a hole formed in the nub portion thus preventing removal of the nub from the mounting face opening.
The above-described mounting apparatus has not, however, proven entirely satisfactory. As rocks or other subject material impinge on the impeller blade during rotation of the turntable, repeated jarring of the impeller block occurs. This, in turn, causes repeated knocking of the block and pin against the upright mounting face of the bracket so that cracks develop in the block, particularly in the nub portion and particularly with time a the hole in the nub portion broadens due to repeated impact with the pin. These cracks may eventually result in the block breaking free from the spinning turntable causing expensive damage to the crusher.
To overcome this problem, other mounting approaches have been tried, each with only partial success. One such approach relies on a pin having an enlarged wedge-shaped head, so that by driving the pin into the hole formed in the nub portion, the back of the block is firmly pressed against the mounting face of the bracket. Despite the initial tight-fit achieved, however, in a short time the pin tends to vibrate back out of the hole, again allowing play between the block and the upright face and possible failure.
Another approach tried has been to bolt the impeller block directly to the mounting face of the bracket using one or more bolts. This approach, however, presents its own difficulties. Due to the heavy wear experienced at the forward face of the impeller, which is sufficient in degree to eventually carve out a deep concave depression in the specially-hardened block, if the relatively softer bolt is run entirely through the block with its head forwardly emerging, the head will quickly wear off causing the block to be thrown from the turntable. Although it would appear that this problem could be readily solved by placing the bolts in threaded bores in the block, in practice, because the block is a specially-hardened alloy that requires casting and is nonmachinable, dimensional matching of the bolt threads with the bore threads cannot consistently be obtained. Thus, the bolts work loose and ultimately fail. A more practical solution is to use heli coils to match the bolt threads, each selected for close seating within the bore that is formed in the particular chosen block, but even here the heli coils have a tendency to pull loose from their seated positions, under repeated jarring of the impeller blocks, eventually causing failure.
An object of the present invention, then, is to provide an improved apparatus for mounting impeller blocks on the turntable of a centrifugal crusher.
A further object of the present invention is to provide a mounting apparatus where repeated jarring or progressive wearing of the impeller blocks, by solid material placed on the turntable, is unlikely to crack the blocks or to cause release of the blocks from the spinning turntable with accompanying damage to the crusher.
A further object of the present invention is to provide an apparatus for mounting impeller blocks on the turntable that does not require the impeller blocks, which are casted of nonmachinable alloy, to be formed precisely to exact dimensional specifications.